1. Field of the Invention
The present invention relates to a propulsion apparatus and a drive apparatus for an endoscope. More particularly, the present invention relates to a propulsion apparatus for an endoscope in which breakage of a wire device can be detected reliably and also operability for propulsion can be maintained, and a drive apparatus for the endoscope.
2. Description Related to the Prior Art
An endoscope is an instrument in the medical field for diagnosis and treatment. The endoscope has an elongated tube and a tip device at a distal end. A CCD or the like is incorporated in the tip device and entered in a body cavity of a patient's body. An image is obtained by the CCD, displayed on a display panel, and viewed for diagnosing the body cavity.
A propulsion assembly for propelling an elongated tube of the endoscope has been suggested recently. U.S. Ser. No. 2005/272,976 (corresponding to JP-A 2005-253892) discloses the propulsion assembly including a support sleeve and an endless track device. The support sleeve is mounted on the tip device of the endoscope. The endless track device is endlessly movable around the support sleeve. An outer run (working run) of the endless track device contacts a wall of a gastrointestinal tract and is traveled, so that the endless track device moves the tip device of the endoscope in a distal direction through the gastrointestinal tract more deeply according to friction of the endless track device with the wall. It is effective in facilitating entry of the endoscope into the gastrointestinal tract of a tortuous form, such as a large intestine, even with low skill in the manipulation of the endoscope.
In U.S. Ser. No. 2005/272,976, wire devices are rotated by motors. A magnet bar is connected at a distal end of the wire devices, and is rotated to move the endless track device endlessly as an extension between magnet rollers. The magnet bar is in a form of windings of which the N and S poles are arranged alternately, and operates as a worm gear. The magnet roller has the N and S poles, and operates as a worm wheel. The wire devices are likely to break with time due to metal fatigue. The endless track device cannot be moved upon breakage of the wire devices. There arises a problem of failure in removal of the propulsion assembly from out of the gastrointestinal tract.
By use of a plurality of the wire devices and a plurality of the motors, the endless track device is still movable by a remaining one of the wire devices when a first one of the wire devices is broken. It is possible to conceive a fail-safe function by detection of breakage of the wire devices. The motors are controlled when the wire devices are broken, for example, the motors are stopped, or driven for moving the endless track device in the proximal direction to eliminate the tip device of the endoscope from the gastrointestinal tract. To this end, rotational speeds of the motors are detected. A speed difference between those is obtained and evaluated to detect breakage of one of the wire devices.
However, the speed difference is likely to occur when the wire devices are flexed, because the rotational speed of the motors is decreased by an increase in the rotational load of the wire devices. Furthermore, resonance vibration of the motors in rotation may occur due to a moment of inertia of the motors and torsional rigidity of the wire devices according to a change in the speed with the flexure of the wire devices. The speed difference of the motors is likely to remain. A problem of poor operability for the propulsion arises when the endless track device is stopped upon detecting breakage of the wire devices with the change in the speed due to the resonance vibration of the wire devices.